Multi-drop, parallel bus implementation is close to its practical limits of performance since it may not easily scale up in frequency or down in voltage; its synchronously clocked data transfer is signal skew limited; and the signal routing rules are at the limit for cost-effectiveness. Approaches to push these limits to create a higher bandwidth, general-purpose input-output (I/O) bus result in large cost increases for little performance gain and diverging standards. At the same time, software applications continue to demand more from platform hardware. For example, streaming data from video and audio sources comprise significant amounts of time-dependent data, putting real-time constraints on computer systems, but the multi-drop, parallel bus I/O architecture of these systems are not designed to handle time-dependent data. As a result, the standards for implementing local I/O bus architecture in a computer system, such as a desktop, server, and notebook, are diverging in an attempt to meet the demands of software applications.
Point-to-point busing may provide sufficiently high-speed data transfers but the problems associated with the architecture are significant. Point-to-point busing is expandable to meet the increasing demands of software, such as the time-dependent data. Unlike multi-drop, parallel buses that have protocols to arbitrate ownership of a bus to a device, such as a peripheral component interconnect (PCI) bus protocol, point-to-point buses, or point-to-point communication arrays, have a dedicated communication medium, or dedicated channels of a communication medium, to transfer data. The dedicated communication medium connects two devices at trace points of the communication medium. More specifically, point-to-point communication arrays provide individual connections between an endpoint device and a hub device, such as an I/O device and chipset, switch, or bridge, without any intermediate wire or connector stubs, since wire or connector stubs cause signal reflections. For instance, when signals at 2.5 gigahertz (GHz) are transmitted between the two endpoints of a link and a device is connected to the link between the source and target devices with wire or connector stubs, the impedance of the device introduces signal reflections that interfere with the signal, preventing interpretation of the signal until the reflections attenuate sufficiently.
Dedicating channels to data transfer between two specific components connected at their trace points, however, has drawbacks such as inflexibility and wasted bus resources, or wasted bandwidth. Unlike the competition and arbitration of ownership between devices connected to a multi-drop, parallel bus, devices attached to dedicated channels do not compete for bandwidth. For instance, when a source device is not transmitting data across a dedicated channel to the full extent of the bandwidth for that channel, the unused bandwidth of that channel is wasted because no other device uses the channel. Further, if the device is removed and not replaced by another device, the entire bandwidth of the channel is wasted. As a result, point-to-point communication arrays are also relatively inflexible with respect to changing device connectivity requirements and changing the number of devices connected to the point-to-point communication array.